You sign up for karate classes. The classes cost \80 per month.
Write an equation for the number of dollars, ddd, that you pay for your karate classes if you take classes for m months.

You are standing next to a really big circular lake. you want to measure the diameter of the lake, but you don't want to have to swim across with a measuring tape! you decide to walk around the perimeter of the lake and measure its circumference, and find that it's 400\pi\text{ m}400? m. what is the diameter dd of the lake?